1. Field of the Invention
The present invention relates to heat exchanger wall construction and a means and method of sealing a heat exchanger wall around an array of heat exchanger tubes.
2. Description of the Prior Art
There are two general classes of heat exchangers in use today. In one class heat is transferred by conduction and the tubes of the heat exchanger carry both the heating or cooling fluid and the fluid to be heated or cooled. In this type of heat exchanger the tubes are soldered, brazed or otherwise attached together to form a number of tubes in a side by side relationship and heat transfer takes place between the walls of the tubes. Alternatively, in this type of heat exchanger, the tubes may be "nested" or cast in a heat transfer medium such as aluminum about and within spaces between the tubes and heat is transferred from the fluid in certain of the tubes through the transfer medium to the fluid which flows in the other tubes. This invention is not directed to this first type or class of heat exchanger.
The second class of heat exchanger in use today transfers heat by convection and employs heat exchanger tubes which are spaced apart in a heat exchanger duct or vessel. There are two types of equipment within this class referred to as tubular heat exchangers and convection sections. In this class of heat exchanger only one of the fluids is pumped through the heat exchanger tubes and the other fluid flows through and around the heat exchanger tubes to accomplish the heat transfer. It is this class of heat exchanger to which the invention is directed.
Conventionally the end walls of a tubular heat exchanger or the end walls of a convection section consist of a solid large flat plate through which a series of openings have been drilled through which the heat exchanger tubes are to pass. A ferrule encircles each tube opening and a heat-resistant refractory material is used on the interior end wall surface between the ferrules. In assembling the heat exchanger the plate is normally vertically oriented and the heat exchanger tubes are inserted one at a time prior to connection.
The diameter of the holes through which the tubes are inserted normally provides a clearance of a minimum of a quarter of an inch and, if finned tubes are used, the area for leakage around the tubes is normally greater than the inner diameter of the tube. This leakage allows a portion of the gases to bypass the heat exchanger tubes by flowing through the head box or manifold cover.
After the tubes have been inserted through the end wall of the heat exchanger a welder must connect the ends of the tubes. Since it is not economical to have the tubes extend very far past the end wall, there is only a small limited space provided for a welder to weld a return bend to the ends of the tubes or to make header to tube welds to the inlet or outlet manifolds. Since the tubes are welded in place, code position welds cannot be conveniently or quickly performed and, as a result, the welding process takes considerable time and becomes a very expensive method of construction because of the "out of position" welds.
In a tubular heat exchanger, in addition to the end walls, intermediate partition baffles are also conventionally used so that the gas in the shell can make a number of passes across the tubes. Conventionally, the portion of these intermediate partitions around the tubes consist of special support castings having heavy flanges for support which are bolted to the frame of the shell baffles. However, the holes in the castings, through which the tubes extend, also have a clearance of a minimum of one quarter of an inch, thereby permitting fluid flow around the tubes and between the partitioned sections of the heat exchanger.